Fuel-air starter and control system therefor



Feb 23, 1960 R. M. s'rEvENs 2,925,713

FUEL-AIR STARTER AND CONTROL SYSTEM THEREFOR Filed Nov. l. 1956 /NVE/VTOR RICHARD M. STEVENS @Y m @@M A T TORNEI/S VUnited States Patent O FUEL-AIR STARTER AND CONTROL SYSTEM THEREFOR Richard M. Stevens, Winsted, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application November 1, 1956, Serial No. 619,894

11 Claims. (Cl. Gil-39.14)

This invention relates to a starter for an aircraft engine or the like and, more specifically, to an improved g-as propelled starter and control system therefor.

It is the general object of the invention to provide a starter of the aforementioned type and a control system therefor which is adapted upon being energized to initiate ow of the components of a combustible mixture and to ignite the mixture to generate gases for starter operation, the system to include means responsive to the said flow and operable after a selected time delay period to shut olf the ignition but to permit flow and combustion to continue until a starting cycle is completed, the said control system also to include means for shuttingr off the iiow when the starting cycle is completed, and the said system also to include means for shutting off the flow in the event that combustion has not started during the time delay period or, having started, the combustion pressure is too high or too low.

The more specific objects and advantages of the invention, as well as the features of construction, will become apparent to those skilled in the art from the following description having reference to the attached drawing wherein, by way of preferred example only, one specific embodiment of the invention is shown. It should be understood that the drawing and the description of the single embodiment shown therein are not to be taken to define or limit the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

In the drawing,

Fig. 1 is a schematic illustration of the starter assembly and the electrical control system therefor; and

Fig. 2 is a sectional view of a pneumatic actuator for the time delay switch forming a part of the starter control structure and system.

In Fig. 1 of the drawing, which is merely schematic, the starter per se is indicated generally by the reference numeral 10 and is shown to be remote from the other components of the starter system, but it should be understood that all of the components and elements of the system can be united in a unitary assembly. The starter 10 is of the type which is gas propelled and includes a turbine 12 disposed in a turbine chamber defined within a housing 14, the said housing also accommodating a gear train 15 which interconnects the turbine 12 with a starter output shaft 16. The gases for propelling the turbine 12 are generated within a generator or combustion chamber 18 and introduced to a suitable turbine nozzle structure through a conduit 20. The gases are discharged from the turbine chamber and from the housing 14 through an outlet 22.

There are a wide Variety of fluid fuels which can be mixed with air to provide a combustible mixture for the combustion chamber 18 and no specific fuel is designated. While the fuel and air can be mixed before introduction into the combustion chamber, in the preferred starter system the fuel is introduced from a source through a conduit 24 and the air is introduced from a pressurized source through a conduit 26. A pump 28 which is driven by an electric motor 29 is provided in the fuel conduit 24 to pressurize the fuel before introduction into the combustion chamber, and a normally closed, solenoid opened shut-0E valve 30 is disposed in the fuel line 24 between the said pump and the combustion chamber. Thus, it can be said that the valve 30 controls ow in the fuel supply conduit 24 which is connected between the gas generator and a pressurized fuel source. There is also a normally closed, solenoid opened valve 32 incorporated in the air conduit 26 between the source and the combustion chamber and an air pressure regulator 34 is provided in the air line between the shutoff valve 32 and the said combustion chamber 18.

While the drawing and description relate specifically to a system wherein there are two supply conduits for the gas generator, one for fuel and one for air, it will be understood that but one conduit and thus but one valve will be needed if the fuel and air are pre-mixed before introduction to the assembly or if a fuel which burns without air is used. In either event, control of the system can be exercised by the elements to be described without material variation as to structure or function.

All of the aforesaid elements of the starter assembly with the exception of the air regulator 34 are either directly or indirectly operated and controlled from a central electrical control panel indicated generally by the reference numeral 36. That is, the motor 29 for the fuel pump 28, and the electrically operated fuel and air valves 30 and 32 are connected in circuits which are energized and de-energized by switch and relay means forming a part of the electrical control and disposed in the panel 36, and the combustion chamber 18 is fired by an igniter 38 which is energized from the said control panel. In addition to the foregoing, there is a speed responsive cut-out switch device 40 associated with the starter output shaft 16 or the gear train thereto, and there is a generally similar cut-out switch device 42 associated with the turbine l2, both of which are included in the electrical control system and electrically connected in the control panel 36. There are also provided as elements of the control system a plurality of pressure responsive switches within a housing 44 which is connected to the combustion chamber 18 through a conduit 46 whereby the said switches will be operated responsive to combustion chamber pressure, the switches being connected in circuits within the panel 36. There is also provided in accordance with the present invention a time delay switch and pneumatic actuator therefor indicated generally at 48 which is responsive to pressure in the air line 26 between the air regulator and the combustion chamber to exercise a control function as part of the electrical system.

The electrical control system comprises a plurality of parallel circuits which are connected with a source of electrical energy through a pair of conductors or lead lines L1 and L2 and the system may be energized and de-energized by operation of a start switch 50 located in one of the said lines. Two of the principal elements of the electrical system comprise a control relay 52 and an interlock relay 54 which are enclosed within the electrical panel 36. When the start switch 50 is closed, the control relay 52 is energized in a circuit whichincludes the normally closed speed responsive switches 40 and 42, a normally closed pressure responsive switch 55 which is disposed in the switch housing 44, a normally closed relay switch 56 which is opened only when the interlock relay 54 is energized, and the two-position time delay switch 48 which is normally in a first position wherein it switch 58 'which kcan vbe opened only when the interlock relay 54 is energized, but a normally open relay 'switch 60 is arranged in parallel `with the switch 58 and is closed when the control relay 52 is energized. Also, whenthe control Yrelay 52 is energized, `a pair ofnormally open switches 62 and 64 controlled thereby are closed in a line to parallel circuits which respectively include the fuel pump drive motor 29, the fuel valve 30, the 'air valve 32, and the igniter 38. The igniter circuit includes a normally closed relay switch -66 which is opened when the interlock relay 54 is energized.

Thus, when the start switch 50 is closed, the control relay 52 is energized and immediately the fuel pump 28 is energized and the fuel and air valves 30 and 32 are opened and the igniter 38 is energized whereby fuel and air will ow to the combustion chamber 18 and be ignited therein. The gases of combustion from the come bustion chamber 18 will be directed through the conduit 20 to the turbine 12 to propel the same and thus to rotate the starter output shaft.

As previously mentioned, it is an object of the present invention to provide means in the control system which will operate automatically at the end of as elected time delay period after fuel flow has been initiated to de energize the igniter while permitting fuel flow and combustion to continue to complete the starting cycle. The means provided for the aforesaid purpose in accordance with the present invention comprises the two-position time delay switch heretofore indicated generally by the reference numeral 48. As shown in the drawing, the switch 48 is normally closed against a switch contact 48a to close the power circuit to the control relay 52. However, the arm of the switch 48 can be moved from its lfirst position in engagement with the contact 48a into its second position in engagement with a contact 48b whereby to close the power circuit which includes the interlock relay 54. When the interlock relay 54 is energized, the normally closed switch 66 in 'the igniter circuit is opened whereby to de-energize the igniter, thus performing one of the aforesaid functions. p

The interlock relay 54 also controls and opens the normally closed switches 56 and 58 in the power circuit to the control relay 52. When the interlock relay is energized it would be expected that .the control relay would be de-energized, thus opening switches 62 and 64 whereby to de-energize the fuel pump and the fuel and air valves to shut olf fuel and air How. However, the switch 58 in the power circuit to the control relay 52 is shunted by the switch 60 which was closed at the time the said control relay 52 was energized. Also, the interlock operated switch 56 will have been shunted from the power circuit to the control relay by means ofa pressure operated switch 68 which is connected to the .control relay circuit in parallel with the time delay switch. The switch 68 is included in the pressure responsive switch housing 44 and is adapted to close if combustion has taken place. That is, the switch 6'8`is adapted to close only in response to a predetermined pressure resulting from proper combustion within the chamber 18. Thus, assuming that combustion has been initiated in the cham.- ber 18 to generate suicient gas pressure for starter operation during the time that the time delay switch `48 is closed in the power circuit to the contro'l relay :52, the subsequent energization of the interlock relay will not de-energize the control relay. Therefore, fuel ipump operation will be maintained and the fuel and air Avalves 30 and 32 will remain open to accommodate continued How to the combustion chamber and :combustion can continue therein. This fu'liills a second function of the time delay switch in the control circuit.

Energization of .the interlock relay A54 also causes .a normally open switch 70 to be closed whereby to vprovide a direct power circuit from line L1 to line L2 through the interlock relay 54 and thus shuntng the 4time delay switch 48 from control of the interlock relay. This ar- 4 rangement makes it necessary to open the start switch 50 before another cycle of starter operation can be undertaken. p

The means for operating the time delay switch so as to move it from its first position in engagement with the contact 48a in circuit with the control relay 52 into its second position in engagement with the contact 48h in circuit with the interlock relay 54 is best shown in Fig. 2. The said means is a pneumatic actuator which comprises a housing 72 dening a pressure chamber 74 having an inlet orifice 76 communicating through a conduit 78 with the airline 26 between the air regulator andthe combustion chamber. It will be understood that when air ow is initiated through the air regulator 34 `and the air conduit 26, air will bleed through the conduit 78 and orifice 76 into the pressure chamber 74. A desired pressure will be established in the air line 26 by the air regulator 34 soon after air flow is initiated, and pressure will build up vin the pressure chamber of the switch actuating chamber 74. Eventually, the pressure within the `chamber 74 will equal the regulated pressure in the air line. At some preselected pressure equal to or less than the said regulated pressure, a diaphragm 80, or its equivalent, in the pressure chamber 74 can be displaced to actuate the time delay switch. The pressure for switch actuation is determined by the selection of the diaphragm or its equivalent which is connected as by a Ilinkage 82 to the switch 48. When the determined or selected pressure is reached, the switch 48 will be moved from engagement with the Contact 48a to engagement with the contact 48h whereby to energize the interlock relay 54 as previously described. At less than the selected pressure, the actuating means Si) biases the switch l48 into engagement with the Contact 48a. Thus, the time delay period taken for the pressure build up within the chamber 74 can be predetermined and/or selected. In this connection it should be noted that the time delay is a function of the volume of the pressure chamber 74, the area of the orifice 76 and the absolute temperature of the air, the regulated pressure of the air in the conduit 26 being substantially constant.

The period of time delay selected should provide suicient time for ignition and combustion within the chamber 18 to generate gases at suiiicient pressure to propel the starter turbine. With sufficient time afforded for combustion to commence, the pressure `of the gases generated will close the pressure responsive switch 68 prior to the time that the time delay switch is actuated to move from its first position to its second position whereby to energize the interlock relay 54. This, of course, assumes that ignition and combustion have taken place. In the event that combustion fails, there will be insufficient gas pressure to close the switch 68 whereby at the end of the time delay period when the interlock relay 54 is energized, the circuit to the control relay '52 will be opened and fuel pump operation will cease and the fuel and air valves will be deenergized and automatically closed to shut down fuel and air flow. Thus, operation of the time delay switch at the end ofthe time delay period will de-energize the control system and avoid wasted fuel and air ow if combustion has not started. Accordingly, the functions of the time delay switch'can be summarized by saying that it shuts ofi ignition at the end of the time delay period while permitting fuel and air flow to continue after combustion is under way, but it conditions the control system to shut olf fuel and airflow and avoid waste and danger if oombustion has not started.

In fulfilling another object of the invention, means lare provided in the control system for automatically de-energizing .the control relay so as to shut olf the fuel pump and close the Yfuel and air valves at the completion of a successful cycle of starter operation. The said means comprises the speed responsive switch 4t) which is normally closed but which can be opened by centif output shaft 16 reaches a selected or desired level.

ugal force or the like when the rotation of the startr n the event of malfunction of the switch 40, the generally similar speed responsive switch 42 which is connected in series therewith will open responsive to turbine speed at a selected level. There is no invention deemed to be involved in the specific form of the speed responsive switches 40 and 42, such devices being commercially 'available and, therefore, the said switches have been shown only diagrammatically.

The switch 55 is incorporated in the control system to fulill another object of the invention, that being to shut down fuel and air ow in the event combustion pressure is excessive. The switch 5S is included in the pressure switch housing 44 and like the switch 68 is diaphragm or bellows operated responsive to combustion chamber pressure. However, the switch 55 is adapted to open only at pressures greater than normal or anticipated combustion pressure and deemed to be excessive and possibly hazardous in starter operation. It is believed that no invention is involved in the specic structure of the pressure switches 68 and 55, these devices being commercially available, and, therefore they have been shown only diagrammatically herein.

Switches 55 and 68 are adapted to be actuated by the combustion pressure of the chamber 18, and to this end are each mounted on a plunger 90 which is in turn secured to the diaphragm 92 located adjacent the bottom of the switch housing 44. To electrically isolate the switches 55 and 68, the plunger 90 is made of a nonconductive material. Each of the switches is adapted to engage elongated contacts mounted on the inner wall of the switch housing, the switch 55 engaging the contacts 94 and the switch 68 engaging the contacts 96. Switches 55 and 68 and the contacts 94 and 96 are each positioned so that the switch 55 remains engaged with the contacts 94 when the switch 68 engages the contacts 96 under the urging of the diaphragm 92. In the event that pressure within the chamber 18 becomes excessive, the diaphragm 92 will be displaced a greater distance upwardly and, while still maintaining the switch 68 against the elongated contacts,96, will disengage the switch 55 from the contacts 94.

Therefore, it can be said that in accordance with the present invention, there is provided a gas propelled starter assembly which includes a gas generator and a control system for the supply of fuel and air to the generator, the said system including pneumatically operated time delay switch means which when actuated normally shuts o ignition while permitting fuel and air ow to continue but which will condition the control system to shut off fuel and air ow in the event that combustion has not been properly initiated, the said system also including means operable to shut olf ow of fuel and air at the end of a starting cycle, and the said system also including means for shutting off the ow of fuel and air if combustion pressures in the gas generator are excessive.

The invention claimed is:

1. In a gas propelled starter for an aircraft engine or the like, the combination comprising a gas generator adapted to burn a combustible uid mixture, a supply conduit connected to the generator and connectible with a pressurized source of an ingredient for combustion, a normally closed electrically opened valve disposed in the conduit, an electrically operable igniter for the generator, and a control system for the starter comprising a plurality of parallel electric circuits which include the valve and igniter, respectively, a pair of conductors for connecting the circuits to a source of energy, a twoposition time delay switch connected to one of said conductors and having a first position to energize said valve and igniter circuits whereby to open the valve and lire the igniter and a second position to de-energize said valve and igniter circuits, pressure responsive actuating means `communicating with said conduit between the valve and generator and connected with said time `delay switch, the said pressure responsive actuating means being adapted to move said time delay switch from said rst position to said second position responsive to but `after a predetermined pressure is established in said conduit, and pressure responsive switch means communicating with said generator and connected to said one conductor in parallel relationship with the time delay switch and adapted when 'closed to energize said valve circuit, the said pressure responsive switch means being normally open and adapted to close responsive to the pressure of combustion.

2. In a gas propelled starter for an aircraft engine or the like, the combination comprising a gas generator adapted to burn a mixture of fuel and air, a pair of supply conduits connected with the generator and respectively connected with pressurized sources of fucl and air, a normally closed electrically opened valve disposed in each of said conduits, an electrically operable igniter for the generator, and a control system for the starter comprising a plurality of parallel electric circuits which include the said valves and igniter, respectively, a pair of conductors for connecting the circuits to a source of energy, a two position time delay switch connected to one of said conductors and having a first position to energize said valve and igniter circuits whereby to open the valves and fire the igniter and a seco-nd position to de-energize said valve and igniter circuits, pressure responsive actuating means communicating with one of said conduits between the valve disposed therein and the generator and connected with said time delay switch, the said pressure responsive actuating means being adapted to move said time delay switch from said first position to said second position responsive to but after a predetermined pressure is established in said conduit, and pressure responsive switch means communicating with said generator and connected to said one conductor in parallel relationship with the time delay switch and adapted when closed to energize the Valve circuits, the said pressure responsive switch being normally open and adapted to close responsive to the pressure of combustion.

3. ln a gas propelled starter for an aircraft engine or the like, the combination comprising a gas generator adapted to burn a mixture of fuel and air, a pair of supply conduits connected with the generator and connectible, rsepectively, with pressurized sources of fuel and air, a normally closed electrically open valve disposed in each of the conduits, an electrically operable igniter for the generator, and a control system for the starter comprising a plurality of parallel electric circuits which include the valves and igniter, respectively, a pair of conductors for connecting the circuits to a source of energy, a two-position time delay switch connected to one of said conductors and having a first position to energize said valve and igniter circuits whereby to open the valves and lire the igniter and a second position to de-energize said valve and igniter circuits, pressure responsive actuating means communicating with the air conduit between the valve disposed therein and the generator and connected with said time delay switch, the said pressure responsive actuating means being adapted to move said time delay switch from said first position to said second position responsive to but after a predetermined pressure is established in said air conduit, and pressure responsive switch means communicating with said generator and connected to said one conductor in parallel relationship with the time delay switch and adapted when closed to energize said valve circuits, the said pressure responsive switch being normally open and adapted to close responsive to the pressure of combustion.

4. In a gas propelled starter for an aircraft engine or the like, the combination comprising a gas generator :adapted ltorburn a fluid mixture, a supply vconduit 'con- 'nected tothe generator and connectible with apres- -'surized source of a uid ingredient 'for combustion, a normally closed electrically opened valve disposed in the conduit, an electrically operable igniter for the generator, and a control system for the starter comprising a plurality of parallel electric circuits and a pair of conductors for connecting the same to va source of electric energy, a Astart switch connected in one of said conductors, a control relay connected in one of said circuits, an interlock yrelay connected in another of said circuits, and other of the said circuits including the valve and the `igniter're spectively, normally open switch means connected in the tvalve circuit and operable by said control relay to close, 'normally closed switch means `connected in the igniter circuit and operable by said interlock relay to open, a two-position time delay switch connected to one of said conductors and having a rst position closing the control relay circuit and a second position `closing the interlock relay circuit, pressure responsive actuating means 'communicating with said vconduit vbetween the valve and the generator and connected with said time delay switch, the said pressures responsive actuating means being adapted to move said time delay switch from -said lirst position 'to said second position responsive to kbut after a predetermined pressure is established in said conduit, and pressure responsive switch means communicating with said generator and connected between said one conductor and the control relay circuit in parallel relationship with said time delay switch, lthe said pressure responsive switch means being normally open and adapted to close responsive to the pressure of combination.

5. In a gas propelled starter for an aircraft engine or the like, the vcombination comprising a gas generator adapted to burn a uid mixture, a supply conduit connected to the generator and connectible with 'a pressurized source of a iluid ingredient 'for combustion, 'a normally closed electrically opened valve disposed in the conduit, an electrically operable igniter for the generator, and a control system for the starter `comprising a plurality of parallel electric circuits and a pair of conductors for connecting the same to a source of electric energy, a starter switch connected in one of said conductors, a control relay connected in one of said circuits, an interlock relay connected in another of said circuits and other of said circuits including the valve and igniter, respectively, normally open switch means connected in the valve circuit and operable by said control relay to close, normally closed switch means connected in the igniter circuit and operable by said interlock relay to open, a two-position time delay switch connected to one of said conductors and having av lirst position closing the control relay circuit and a second position closing the interlock relay circuit, pressure responsive actuating means communicating with-said conduit between the valve and the generator and connected with said time delay switch, the said pressure responsive actuating means being adapted to move said time delay switch from said one position to said other position responsive to but after a predetermined pressure is established in said conduit, pressure responsive switch means communicating with said generator and connected between said one conductor and the control relay circuit in parallel relationship with said time delay switch, the

said pressure responsive switch being normally open and adapted to close responsive to the pressure of combustion, and a normally open switch connected between'said one conductor and said interlock relay and which is adapted to be closed by said interlock relay.

6. In a gas propelled starter for an aircraft engine or the like, the combination comprising a gas generator adapted to burn a fluid mixture, a supply -conduit connected to the generator and connectible with a pressurized source of a iluid ingredient for combustion, a normally .closed electrically opened valve-disposed in the conduit, an electrical]y operable vigrliter for the generator, and a control 4'system for the starter `comprising a Eplurality `of parallel electric circuits Awhich 2include 'the -valve and igniter, respectively, a pair vot conductors for con- -necting the circuits toa source of energy, a two-position time delay 'switch connected to `one of 'said conductors and having a lfirst position to energize said valve l'and igniter circuits whereby lto open the valve and fire the -igniter and -a second vposition toile-:energize said valve and igniter circuits, pressure responsive actuating 'means communicating with said conduitbetween the valve and generator and connected with said time delay S'Witch,'the said pressure responsive actuating means being adapted to move said Itime -delay switch from `said first position to said second lpositionresponsive to but after a-predetermined vpressure is establishedin said conduit, pressure responsive switch means communicating `with said 'generator and connected to said one conductor in parallel relationship with the vtime delay switch `and adapted when closed to energize said valve circuit, the saidpressure responsive switch means being normally 'open and adapted to close responsive to :the pressure of combustion, and normally closed speed responsive switch `means operated by the starter for de-energizing said valve -circuit, said speed responsive switch lmeans being adapted to open at a "predetermined starter speed.

7.l In a gas propelled starter -for 'an vaircraft engine or the like, the combination comprising a gas 'generator adapted to burn a `iinid mixture, a supply conduit connected to the generator `and connectible with a ,pressurized source of a uidy ingredient for combustion, a "normally closed electrically opened valve disposed in the conduit, an electrically operable-igniterfor the generator, and a control system for the starter comprising a plurality of parallel electric circuits which include kthe valve and igniter, respectively, a lpair of conductors for Connecting the circuits to a source of energy, a two-position time delay'switch connected to `one `of said conductors and having a first position to energize Isaid valve and igniter circuits whereby `to open the valve and tire' the igniter and a second position to de-energize said' valve and igniter circuits, pressure responsive actuating means communicating with said conduit between the valve and generator and connected with said `time delay switch, the said pressure responsive actuating means being adaptedto move said time delay vswitch Vfrom` said tirst position to said second position responsive to but after a lpredetermined pressure is established in said circuit, pressure 'responsive switch means communicating with said generator and connected to said one `'conductor 'in Aparallel relationship with the time delayswit'ch and adapted when closed to energize said valve circuit, the said pressure responsive switch means being normally open and adapted to yclose responsive to the pressure of combustion, and second pressure responsiveswitch means communicating-with said 'generator for de-'e'nergizing said valve circuit, said second pressure responsive `switch means being normally closed and adapted toopen re` sponsive to pressure in said lgenerat'o1"`in excess yofnormal combustion pressure.

8. In a gas propelled starterfor an aircraft engine vor the like, the combination comprising a gas lgenerator adapted to burn afiiuid mixture, a supply conduit connected to the generator and connectible with a pressurized source of a liuid ingredient for combustion, a normally closed electrically opened `valve disposed'in the conduit, an electrically operable igniter for the generator, and a control system for the starter comprising axplu'r'ab ity of parallel electric circuits -which include the valve and igniter, respectively, a -pair of conductors orlconnecting the circuits -to `a source of energy, a two-position time delay switch connected toone of said conductorsand 'having a first position to energize vsaid valvel-and igniter circuits whereby to open -the va'lveand lire the' ignitei and a second position to le-'energize said valve asesina and igniter circuits, pressure responsive actuating means communicating with said conduit between the valve and generator and connected with said time delay switch, 'the said pressure responsive actuating means being adapted to move said time delay switch from said iirst position to said second position responsive to but after a predetermined pressure is established in said conduit, pressure responsive switch means communicating with said generator and connected t said one conductor in parallel relationship with the time delay switch and adapted when closed to energize said valve circuit, the said pressure responsive switch means being normally open and adapted to close responsive to the pressure of combustion, normally closed speed responsive switch means operated by the starter and adapted to de-energize said valve circuit, said speed responsive switch means -being normally closed and adapted to open at a predetermined starter speed, aud second pressure responsive switch means communieating with said generator and adaped to de-energize said valve circuit, said second pressure responsive switch means being normally closed and adapted to open responsive to pressure in the generator in excess of combustion pressure.

9. In a gas propelled starter for an aircraft engine or the like, the combination comprising a gas generator adapted to burn a uid mixture, a supply conduit connected to the generator and connectible with a pressurized source of a uid ingredient for combustion, a normally closed electrically opened valve disposed in the circuit, an electrically operable igniter for the generator, and a control system for the starter comprising a plurality of parallel circuits which include the valve and igniter, respectively, a pair of conductors for connecting the circuits to a source of energy, a two-position time delay switch connected to one of said conductors and having one position to energize said valve and igniter circuits whereby to open the valve and re the igniter and a second position to de-energize said valve and igniter circuits, a pneumatic actuator for said time delay switch comprising a housing dening a chamber having an orifice in communication with said conduit whereby to establish a pressure in said chamber equal to a pressure established in said conduit but after conduit pressure is established, pressure responsive actuating means disposed in said chamber, and connected to said time delay switch and adapted normally to hold said time delay switch in said first position and to move the same to its second position responsive to increased pressure in the said chamber, and pressure responsive switch means communicating with said generator and connected to said one conductor in parallel relationship with the time delay switch and adapted when closed to energize said valve circuit, the said pressure responsive switch means being normally open and adapted to close responsive to the pressure of combustion.

10. In a gas propelled starter for an aircraft engine or the like, the combination comprising a gas generator adapted to burn a mixture of fuel and air, a pair of supply conduits connected with the generator and respectively connected with pressurized sources of fuel and air, a normally closed electrically opened valve disposed in each of said conduits, an electrically operable igniter for the generator, and a control system for the starter comprising a plurality of parallel electric circuits which include the said valves and igniter, respectively, a pair of conductors for connecting the circuits to a source of energy, a two-position time delay switch connected td one of said conductors and having a rst position to energize said valve and igniter circuits whereby to open the valves and fire the igniter and a second position to de-energize said Valve and igniter circuits, a pneumatic actuator for said time delay switch comprising a housing defining a chamber having an orifice in communication with said air conduit between its valve and the generator whereby to establish a pressure in said chamber equal to a pressure established in said air conduit but after conduit pressure is established, pressure responsive actuating means disposed in said chamber and connected to said time delay switch and adapted to hold said time delay switch in the said tirst position and to move the same to its second position responsive to increased pressure in the said chamber, and pressure responsive switch means communicating with said generator and connected to said one conductor in parallel relationship with the time delay switch and adapted when closed to energize the valve circuits, the said pressure responsive switch means being normally open and adapted to close responsive to the pressure of combustion.

11. In a gas propelled starter for an aircraft engine or the like, the combination comprising a gas generator adapted to burn a uid mixture, a supply conduit connected to the generator and connectible with a pressurized source of a fluid ingredient for combustion, a normally closed electrically -opened valve disposed in the conduit, an electrically operable igniter for the generator, and a control system for the starter comprising a plurality of parallel electric circuits and a pair of conductors for connecting the same to a source of electric energy, a start switch connected in one of said conductors, a control relay connected with one of said circuits, an interlock relay connected in another of said circuits, and other of said circuits including the valve and igniter, respectively, normally open switch means connected in the valve circuit and operable by said control relay to close, normally closed switch means connected in the igniter circuit and operable by said interlock relay to open, a two-position time delay switch connected to one of said conductors and having a rst position closing the control relay circuit and a second position closing the interlock relay circuit, a pneumatic actuator for said time delay switch comprising a housing defining a chamber having an orifice in communication with said conduit between the valve and the generator whereby to establish a pressure in said chamber equal to a pressure established in said conduit but after conduit pressure is established, and pressure responsive actuating means disposed in said chamber and connected to said time delay switch and adapted normally to hold said time delay switch in its said rst position and to move the same to its second position responsive to pressure in the said chamber, and pressure responsive switch means communieating with said generator and connected between said one conductor and the control relay circuit in parallel relationship with said time delay switch, the said pressure responsive switch means being normally open and adapted to close responsive to the pressure of combustion.

Fleming et al. Aug. 16, 1955 Kelly Apr. 24, 1956 n Attest:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,925,713 February 23v 1960 Richard M, Stevens It is hereby certified that error appears in theprlinted specification of -the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 231I for "as electedH read a selected --5 column 6, line 48 for "rsepectively" read respectively column 7, line 23, for "pressures" read pressure u; line 32, for "combination" read combustion Signed and sealed this 2nd day of August 1960 (SEAL) KARL H AXLINE ROBERT C. WATSON Attesting Officer v Commissioner of Patents 

